This invention relates to the medical procedure of angioplasty, and more particularly to angioplasty performed in a cyclic manner which may be synchronous with the rhythm of the heartbeat.
Several hundred thousand people die in the United States each year from acute myocardial infarction, and many more suffer from chronic heart problems. A major contributing factor in both acute and chronic heart problems is a reduction ill nutrient blood flow to the muscles of the heart resulting from a reduction of blood flow through the coronary blood vessels. The reduction in flow may be caused by deposits of atherosclerotic plaque on the walls of the blood vessel, which causes a narrowing of the lumen or channel of the blood vessel. When the lumen is sufficiently narrowed, the rate of flow of blood may be so diminished that spontaneous formation of a thrombus or clot occurs by a variety of physiological mechanisms. As is known, once a blood clot has started to develop, it extends within minutes into the surrounding blood, in part because the proteolytic action of thrombin acts on prothrombin normally present, tending to split this into additional thrombin which causes additional clotting. Thus, the presence of atherosclerotic plaque not only reduces the blood flow to the heart muscle which it nourishes, but is a major predisposing factor in coronary thrombosis.
Among the treatments available for the conditions resulting from plaque formations are pharmacological means such as the use of drugs, for example nitroglycerin, for dilating the coronary blood vessels to improve flow. Surgical treatment may be indicated. One of the surgical techniques commonly used is the coronary bypass, in which a substitute blood vessel shunts or bypasses blood around the blockage. The bypass operation is effective but is expensive and subject to substantial risks.
A technique which has recently received a good deal of attention is transluminal laser catheter angioplasty. This treatment involves introduction into the coronary artery of a fiber optic cable, the proximal end of which is connected to a laser energy source. The distal end of the fiber optic cable is directed toward the plaque. The laser is pulsed, and the resulting high energy light pulse vaporizes a portion of the plaque. Many problems remain unsolved in laser catheter angioplasty, such as matching the characteristic of lasers and fiber optic cables to the frequency absorption characteristics of various types of plaque, and the by-products of the destruction of the plaque.
Percutaneous transluminal balloon catheter angioplasty is an alternative form of treatment. In general, an angioplasty procedure is performed by obtaining access to the interior of a coronary artery partially obstructed by plaque, and advancing a deflated balloon to the location of the stenosis. The balloon is inflated by applying fluid pressure through an inflation/deflation ("inflation") lumen of the catheter, to thereby apply balloon pressure tending to expand the lumen of the coronary artery. When the stenotic portion of the lumen of the blood vessel or coronary artery has about the same diameter as adjacent portions which are free from plaque, the procedure may be terminated, the balloon deflated and the catheter removed. The lumen remains expanded after removal of the catheter. It has been observed, as mentioned in the article entitled "Perfusion During Coronary Angioplasty," by Rossen, published at pages 103-106 in the June 1989 issue of Cardio, that increased time with the balloon inflated is associated with an improved result, which is to say that the longer the stenotic region remains dilated by the balloon, the more likely it is to stay open. The art relating to angioplasty includes many advances, such as the microwave-aided angioplasty described in U.S. Pat. No. 4,643,186, issued Feb. 17, 1987 in the name of Rosen et al., which heats the affected region to aid in softening the plaque to allow it to expand more readily under balloon pressure.
Those portions of the heart muscle supplied with blood flow through the artery are at least partially deprived of blood flow when the catheter with deflated balloon is being positioned in the stenotic region, and may be completely deprived of blood flow when the balloon is inflated. This in turn has a tendency to decrease heart pumping efficiency, and the blood pressure tends to drop. Chest pains result in some patients. Either of these indications may undesirably require early termination of the procedure, which may produce a less than optimal result.
Dilatation catheters are available, as described in the above-mentioned Rossen article, in which perfusion or blood flow past the occluding catheter and balloon is provided by fenestrations or apertures into the distal lumen of the catheter on both sides of the balloon. Such perfusion catheters tend to be somewhat larger in diameter and stiffer than conventional catheters having the same inflated balloon diameter, and are therefore more difficult to position. Also, their larger diameter excludes them from use in the small arteries into which conventional balloon catheters may fit. Another type of perfusion catheter, described in U.S. Pat. No. 5,108,370, issued Apr. 28, 1992, in the name of Walinsky, includes an annular or toroidal balloon defining a central perfusion aperture, through which blood can flow while the balloon is inflated, thereby allowing nutrient blood flow to tissues located downstream of the balloon.